Many known agrochemicals have shown to be more effective in combination than when applied individually.
Herbicides, and in particular glyphosate, are usually sprayed in combination with organic adjuvants (such as surfactants acting as wetting agents and stickers) and inorganic adjuvants (such as inorganic nitrogen or potassium containing fertilizers). The presence of the various adjuvants guarantees good phytoactivity and avoids detrimental and/or unpredictable effects due to local conditions (water hardness, soil quality, weather conditions, etc).
Various systems have been devised for convenient dosing of agrochemicals, such as herbicides, on field, crop area, plants etc., for example spray pumps which spray diluted agrochemical formulations (tank mix) from a opportune manifold onto the area of land or crop area, or more complex apparatus which are designed to dose concentrated agrochemical formulations into the pump and to mix them with water before being sprayed.
During the spraying of agrochemicals, it is necessary to add anti-drift agents (drift control agents) in order to prevent the formation of fine droplets, which could be carried beyond the area intended to be treated. Without the use of anti-drift agents, the spraying could be largely inefficient, first of all because there could be an inadequate treatment of the land and crop areas to be treated and secondly because the extraneous spray, if carried beyond the intended treatment zone, could be detrimental to other crops, land and water courses.
Typical drift control agents are synthetic or natural polymers such as polyacrylamides, polyethylene oxides, polyvinyl pyrrolidones, guar gum and guar gum derivatives. In particular in the agriculture industry, polyacrylamides and guar gum and its derivatives are the standard additives for spray drift control.
It is usual to combine the anti-drift agent in the agrochemical formulations diluted for the spray application (tank-mix). Alternatively the anti-drift agent is dissolved in either the water which is fed into the spray pumps or applied directly into the spray pumps, usually at or shortly after the mixing zone where the water is mixed with the herbicide, pesticide or aqueous fertilizer concentrate. It is important that the spray drift chemical is correctly dosed and well dissolved to ensure that extraneous spray is not formed through under dosing or through overdosing or the spray angle is too narrow resulting in uneven distribution of the agrochemical.
However, these procedures have the problem that polymers, such as polyacrylamides, guar and guar derivatives, can be difficult to activate in field situations and polymer powders take a long time to dissolve. This can lead to the formation of gel particles which can block in-line screens and nozzles, resulting in pressure buildup in the system and spotty spray patterns.
A good solution to this problem could be dissolving/dispersing an adequate amount of anti-drift agent directly in the agrochemical concentrates. However, it is really difficult to dissolve sufficient polymer in the concentrates without obtaining solution with an unacceptable or unmanageable viscosity and/or to obtain stable solutions to achieve adequate spray drift in all cases. Furthermore, the types of polymeric anti-drift agents will be limited to the few which are easily soluble in the compositions to give adequate spray drift properties.
It is well known in the art that it is possible to prepare stable suspensions/dispersions of polysaccharides in concentrated solutions of electrolytes, such as ammonium or alkali salts of sulfate, nitrate and phosphate. These suspensions/dispersions are described for example in U.S. Pat. No. 4,971,728, U.S. Pat. No. 4,272,414 and U.S. Pat. No. 6,322,726, but none of these patents describes an adjuvant composition containing also a high amount of surfactant(s).
Suspensions/dispersions of polysaccharides in solution of electrolytes and surfactants are described in U.S. Pat. No. 4,883,537, U.S. Pat. No. 5,898,072, EP 413274 and US 2011/0054042 and EP 2606724.
US 2011/0054042, for example, describes compositions containing ammonium sulfate at concentration around 25-30% by weight and HPG at a concentration around 2-6% by weight and an alkyl betaine in the presence of a suspending agent, typically fumed silica, and/or a water soluble organic solvents.
U.S. Pat. No. 6,364,926 describes concentrated liquid adjuvant compositions comprising, by weight of the composition: a) about 25% to about 35% of a nitrogen compound in the form of an ammonium salt; b) about 0.1% to about 5% of an ampholytic surfactant, c) about 0.1% to about 2.5% of a drift control agent/deposition aid (hydroxypropyl guar), and d) about 55% to about 75% of a carrier. In this adjuvant concentrate both fertilizers and surfactants are present, but the concentration of drift control agent is quite low and does not allow high dilutions of the concentrates.
However these suspensions/dispersions are metastable systems and require the addition of a suspending agent for stabilization.
Unfortunately suspending agents are usually thickeners, such as clays, fumed silica or polymeric thickening agents, which further increase the viscosity of the suspensions/dispersions, reducing on-field manageability of the adjuvant compositions.
Alternatively, particular and time consuming methods of dissolution were developed, as described in EP 2606724 which discloses an aqueous adjuvant concentrate with improved spray drift properties and method for its preparation comprising the steps of: i) dissolving from 15 to 30% by weight, on the weight of the final concentrate, of ammonium sulfate in water; ii) adding to the solution from 1 to 10% by weight, on the weight of the final concentrate, of anionic esters of alkyl polyglycosides; iii) dispersing in the solution from 2 to 10% by weight, on the weight of the final concentrate, of hydroxypropyl guar or hydroxypropyl guar acetate; iiii) adding ammonium sulfate to the dispersion to reach an ammonium sulfate final concentration comprised between 33 and 40% by weight.
We have now discovered that stable and low viscosity aqueous adjuvant concentrates comprising, dissolved therein, up to 9% by weight of a hydroxypropyl tamarind gum (HPT) as anti-drift agents, from 15 to 45% by weight of potassium salts and up to 6% by weight of surfactants can be easily prepared, also without the use of a suspending agent or complex method of preparation. These concentrates contain high amount of dissolved adjuvants and anti-drift agent, are stable also in difficult environmental conditions, and, at the same time, they are easily pourable and manageable. For these reasons, they can be used to prepare directly in locus diluted sprayable herbicidal formulations, in particular glyphosate based formulations, with excellent anti-drift characteristics.